Wide band direction finder antenna



April 11, 1967 DUBOST 3,314,069

WIDE BAND DIRECTION FINDER ANTENNA Filed May 6, 1964 2 Sheets-Sheet 1(A') (A) (A) (A) 0 9 6 :9 f Fl 6.. 2 FIG. 5'

PR/OR ART PRIOR ART l i i f 1 2 L A: COUPLER PHASE SHIFTING l l 37 4NETWORK H64 Flt-3.5 a?

RECEIVER 5 A P A W I 1 COUPLING COUPLING CIRCUIT CIRCUIT FIGJ L I Y IRECEIVER V3 I UM Apnl 11, 1967 G. DUBOST WIDE BAND DIRECTION FINDERANTENNA 2 Sheets-Sheet 2 Filed May 6, 1964 vita E ESQ V II IllluV UnitedStates Patent WIDE BAND DIRECTION FINDER ANTENNA Grard Dubost, Paris,France, assignor to CSF-Compagnie Generale de Telegraphic Sans Fil, acorporation of France Filed May 6, 1964, Ser. No. 365,434 Claimspriority, application France, May 7, 1963, 933,896; Apr. 28, 1964,972,593, Patent 85,806 6 (Ilaims. (Cl, 343-119) The present inventionrelates to broad-band direction finder systems, comprising two identicaldirectional antennas or arrays of generally regularly spaced antennas.To determine a direction, the two radiation patterns have to besymmetrically inclined with respect to the bisector plane normal to theline joining the respective radiation centers. Generally the radiationpatterns are inclined by an angle, which is constant whatever theoperating frequency. However, this results in that, in the defineddirection, the gain of each array varies to a substantial degree withfrequency and the precision with which a direction is defined is quitevariable.

It is an object of this invention to avoid this drawback. To this endthe invention provides a circuit for dividing the energy fed to eacharray between the antenna elements building up this array with suchrelative phase shifts between the antenna elements that the ratio of thegain, in the direction defined by the system to the maximum gain of onearray, remains constant within a wide band of frequencies.

The invention will be better understood from the following specificationand appended drawings wherein:

FIG. 1 shows, very diagrammatically, a direction finder system accordingto the invention;

FIGS. 2 and 3 illustrate the gain variations of a conventional directionfinder antenna system for two different frequencies;

FIG. 4 illustrates the phase shift between two antennas of an antennasystem according to the invention as a function of the operatingfrequency for a uniform distribution of the applied energy between theelements of the array.

FIG. 5 shows one array of the antennas of. a system according to theinvention; and I FIG. 6 shows an array according to the inventioncomprising n antenna elements.

The system shown in FIG. 1 comprises two directive identical antennaarrangements A and A of identical antenna elements a a and a' a' Line pis the trace on FIG. 1 of the plane with respect to which the twoarrangements are symmetrical. The antenna elements a and a or a' and aare paced by d. The antenna elements of arrangement A are connected to-a coupling circuit 5 and the antenna elements of arrangement A areconnected to a coupling circuit 5. The arrangements A and A aredirective and their radiation patterns form an angle a. The couplingcircuits 5 and 5 are respectively connected to the two inputs of agoniometric re ceiver 3.

In FIG. 2, the gain G of the two antenna arrangements has been plottedalong the ordinates vs. the angle of the direction of the incomingsignal, for a given inclination angle at of the radiation patterns andfor a given frequency.

The direction defined by the abcissa 0 i.e. by the intersection of thetwo radiating patterns, is the direction of the transmitter or reflectorwhere the received signal originates. The gain in that direction is g InFIG. 3 the same plots were made for another frequency f, all otherthings being equal.

It may be readily seen that, in spite of an increased directivity, thegain in the direction 0 has decreased.

3,314,069 Patented Apr. 11, 1967 Accordingly the precision with whichthe direction is defined also varies as a function of the frequency.

Thus, with the conventional practice of keeping constant the inclinationof the radiating lobes with respect to their plane of symmetry, which isobtained by making the relative phase shifts between the antennaelements of each array proportional to the operating frequency, the gainof the antenna system in a given direction, and accordingly theprecision, vary to a substantial degree. In this respect, it may beshown that the amount of energy P received in the direction defined bythe intersection of the two diagrams as shown in FIGS. 2 and 3, andaccordingly the gain, other things being equal, varies substantially asthe product (p, f, g0 being the relative phase shift between the antennaelements of an array and f the frequency and it being assumed that eachantenna receives the same energy amount. If (p is made proportional to1, gain G varies as f i.e. highly variable with frequency.

If, however, under the same power distribution, [gel is made to decreasewhile increases, the gain will practically not vary with the operatingfrequency. The in- 'clination of the lobes with respect to their planeof symmetry will then vary with the operating frequency, but this is nota drawback. If f is made to decrease linearly when 1 increases, asubstantial constancy of the gain in the direction defined will beobtained.

In FIG. 4, (,0 has been plotted along the ordinates and 1, which variesbetween values f1 and f2, along the abcissae, still in the abovementioned case of uniform power distribution between the antennaelements of the array.

FIG. 5 shows an arrangement according to the invention in the same case,the array comprising two antenna elements.

Antenna a feeds the input and antenna a feeds the 0 input of a 90directional coupler 1 through a phase shifting network 2.

The output of coupler 1 is connected to receiver 3. A suitable loadimpedance 4 is connected to coupler 1. Network 2 can be of the low passor high pass type depending on the purpose the aerial system serve-s.

'Network 2 introduces a phase shift which, together with the phase shiftof the transmission lines needed in the circuit which varies with thefrequency may be for all practical purposes, considered to beproportional to the operating frequency.

The signals picked up by the antenna element a are thus received byreceiver 3 with no phase shift (reference shift) while those picked upby the antenna element a are picked up with a phase shift 90+kf, k beingselected such that, in the operating frequency range, -90+kf isnegative. Coupler 1 may be of any type, provided it insures between theinputs and the outputs a 90. phase-shift of one of the signalsrelatively to the other.

By way of example, antennas A and A may each comprise two elementaryantennas covering about one octave between 2.3 to 4.3 gc./s., with a cos0 radiation pattern, the antennas being spaced by 59 mm., the phaseshift between the elementary antennas passing from 93 to 53? in absolutevalue as the frequency varies fro-m 2.3 to 4.3 gc./s. and the maximumgain variation in the defined direction being :0.5 db, with a gain ofabout 2 db below the maximum.

In the most general case, i.e. when the distribution of power betweenthe several antenna elements of each array is not uniform, the relativephase-shifts between these elements have to vary in different manners asa function of the frequency.

FIG. 6 shows an embodiment of the invention which makes it possible tovary the phase-shift between any two adjacent antenna elements of thearray according to the power amounts respectively radiated by the same.The arrangement is assumed to be a receiver arrangement. Of course thediagram would be the same with an emitter arrangement except that thedirection of the arrows has to be reversed and transmitters have to besubstituted for the receivers.

FIG. 6 shows an array of n antennas A1 to An. The array feeds the inputof a goniometric receiver R.

The circuit comprises n1 arrangements, each of them comprising in seriesa phase-shifting network Pi, with i equal to 1 to 11-1, coupled to thefirst input of a directional coupler Ci. The n-l arrangements areconnected in series in such a manner that a first output of each coupleris coupled to the input of the adjacent network Pi. The output ofnetwork Pi is coupled to the first input of coupler Ci, and the firstoutput of coupler Ci except for coupler C1, is connected to the input ofnetwork Pi1. The first input of coupler C1 is connected to receiver R.

Antenna elements A1 to A 1 are respectively connected to the secondinput of couplers Ci through a suitable transmission line Li whileantenna An is directly coupled to network Pn-l. The second outputs ofcouplers Ci are grounded through respective matched loads ri. Thetransmission lines Li connect the elementary antennas Ai to couplers Pi.

By way of example, the following characteristic values were used in anarrangement according to the invention including two arrays of threeantennas. The arrangement was operated successfully in a frequency bandfrom f =4.3 gc./s. to f2 6.9 gc./s.

The reference number (used hereinafter are those of FIG. 6, with 11:3).

Phase-shifting network P1 introduces a phase-shift varying from $+31 ath, to -31 at f phase-shift network P2 introduces a phase-shiftingvarying from +7 at f to 7 at f C1: 4.8 db coupler C2: 3 db coupler L1and L2: conventional connection transmission lines.

Under these conditions, antennas A1 or A3 radiate the same energyamount, equal to half the power radiated by antenna A2 and the relativephase shifts between the antennas are maintained constant and equal to60 between antennas A3 and A2 and -60 between antennas A1 and A2. Thevariations of the phase-shifts introduced by networks P1 and P2 thuscompensate the variations due to the transmission lines and thecouplers. The gain in the defined direction was maintained 3 db belowthe maximum gain.

Of course, the invention is not limited tothe embodiment described andshown which were given solely by way of example.

What is claimed is:

1. A wide-frequency band direction finder system comprising a first anda second directive array of elementary antennas, said arrays havingidentical radiation patterns with the same maximum gains and defining agiven direction, and means for maintaining constant, within a given bandof operating frequencies, the ratio of the respective gains of saidarrays in said direction to said maximum ain. g 2. A wide-frequency banddirection finder system comprising a first and a second directive arrayof elementary antennas and phase shifting means providing a phase shiftbetween adjacent elementary antennas, whose absolute value decreases asthe operating frequency increases.

3. A wide-frequency band direction finder system comprising a first anda second directive array of elementary antennas and means for couplingadjacent antennas to each other, said means comprising in series adirectional coupler having at least a first, a second and a thirdterminal, the energy amount at said third terminal being equal to thesum of the energy at said first and second terminals with a relativephase-shift of therehetween, and a phase-shifter whose phase-shift isfrequency responsive, said adjacent antennas being coupled to saidphase-shifter and to one of said first and second terminalsrespectively.

4. A wide frequency band direction finder system comprising: a first anda second directive array each of them comprising a first and a secondantenna, a goniometric receiver, and a first and a second circuit forrespectively coupling said receiver to said first and second arrays,each of said circuits comprising: a junction having a first in- .put, asecond input coupled to the first antenna and an output coupled to saidreceiver, means for coupling said second antenna to said first input,said means comprising a phase shifting network, whose phase shiftcharacteristic is, in absolute value, a decreasing function of theoperating frequency.

5. A wide frequency band direction finder system comprising: a first anda second directive array, each of them comprising a first and a secondantenna, a transmitter, and a first and a second circuit for couplingsaid transmitter respectively to said first and second arrays, each ofsaid circuits comprising: a junction, having an input coupled to saidtransmitter, a load, a first output corresponding to said input, asecond output coupled to said first antenna, and means for coupling saidfirst output to said second antenna, said means comprising a phaseshifting network, Whose phase shift characteristic is in absolute valuea decreasing function of the operating frequency.

6. A wide frequency band direction finder system comprising a first anda second directive identical array of n adjacent elementary antennas,where n is an integer greater than one, and a first and a second circuitfor respectively feeding said first and second arrays, each of saidcircuits comprising: n1 90 couplers having respective first inputs,respective second inputs, respective first outputs and respective secondoutputs; n1 respective transmission lines for respectively coupling then-l first antennas of the array to said second inputs of said couplers,n 1 matched loads for respectively grounding said second outputs of saidcouplers, n1 phase-shifting network having respective inputs andrespective outputs respectively coupled to said first inputs of saidcouplers, means for cascade coupling said phase shifting networks andsaid couplers by their respective inputs and outputs having the samenumber and means for coupling the nth antenna to said input of saidn-lst network.

References Cited by the Examiner UNITED STATES PATENTS 5/1964 Takagi etal. 3/ 1966 Vogt.

2. A WIDE-FREQUENCY BAND DIRECTION FINDER SYSTEM COMPRISING A FIRST ANDA SECOND DIRECTIVE ARRAY OF ELEMENTARY ANTENNAS AND PHASE SHIFTING MEANSPROVIDING A PHASE SHIFT BETWEEN ADJACENT ELEMENTARY ANTENNAS, WHOSEABSOLUTE VALUE DECREASES AS THE OPERATING FREQUENCY INCREASES.